This invention relates generally to electromagnetic linear actuators and more specifically to a mechanical suspension system for such actuators.
Electromagnetic linear actuators commonly referred to as linear force motors or force motors require a suspension system which imposes a well defined, bi-directional force between the stator and armature of the linear force motor. Such a suspension system normally requires the force vector to be applied in a co-linear manner with the axis of motion of the force motor armature. In addition, the magnitude of force which is applied by the suspension system is, in general, linearly related to the relative displacement between the stator and the armature of the force motor. Furthermore, it is usually required that the suspension system must be capable of adjustment, so that the null or zero magnitude force can be imposed for any given relative position between the stator and armature of the force motor.
Traditionally the requirements for the suspension system of linear force motors has been met through the utilization of helical springs which are applied to one or both ends of the force motor armature. The utilization of such springs generate a number of problems. First of all, when one spring is located on each side of the reciprocating armature the overall length of the reciprocating motor can be excessive and the device cannot be utilized in areas where space is at a premium. In addition, adjustment is often difficult since each side of the motor must be accessible for that purpose. However, when the springs are both located on one end of the armature the containment mechanism is complex in order to provide the appropriate adjustment capabilities. In addition to the foregoing, when a helical spring suspension system is utilized, some modicum of loading must be maintained to cause the suspension system to work properly. This is required to prevent unloading for bi-directional motion about a neutral position. Such preloading creates an undesirable sustained stress in each member of the suspension system, and such stress must also be subject to appropriate control and adjustment, which further complicates the situation.
The best prior art known to applicant are U.S. Pat. Nos. 2,264,902, 2,939,663 and 3,067,404.